After having got through the two Schemer books, I'm about to embark on HtDP but also discovered the http://docs.plt-scheme.org/guide material.
The previously mentioned books are more particular to Scheme, it seems, and the latter being more geared towards PLT specific extensions (modules, require, bracket syntax, etc...). The online manual is excellent but I was hoping there might be a book form that I could purchase?
If not, I'm certainly grateful for the in-depth online manual - was just curious!
No, I don't believe so. The only other PLT-specific book that's in print right know (AFAIK) is the excellent "Semantics Engineering with PLT Redex", but I don't think that's what you're looking for. You might also be interested in Krishnamurthi's Programming Languages: Application and Interpretation. Both of these are targeted at programming languages folks.